• Watch directories exclusively as this is the only viable cross-platform compatible method unless the user set KDEV_PROJECT_INTREE_DIRWATCHING_MODE.

When watching directories, take into consideration that 1) a notification can come from a new or changed hidden file; 2) many changes can be signalled in rapid succession and 3) notifications are about changes in the given directory (= not in any of its subdirs).
Nothing can be done about 1) but the other 2 points are taken into account:

• queue reloads (with a rather arbitrary 1s cool-off delay) instead of starting them at once.
• reloads due to change notifications are marked disposable
• when another notification arrives for a directory that's already reloading (or scheduled for), abort the current job(s) where possible (or skip the directory if it's a subdir) before creating the new job. Consider only "disposable" jobs for this.
• when the notification is about an already known directory the reload will be non-recursive.
• file manager list jobs are registered with the RunController.

Does what it's intended to do, tested while running configure on a bigger in-tree build project (e.g. CodeBlocks).
Dir watching works also on Mac if you don't set watches on all files; the effect of reload-limiting is clear from following CPU usage in top, from fan noise, and from the RunController buttons turning on in the toolbar for only short periods of time.

Tested on Mac and Linux.